Google's recommendations for multilingual sites say that:
But they use them for all their services like:
support.google.com... Just try to add
hl=xx to the URL and the language will be changed. They don't use subdomains or subdirectories. Sometimes they use top level domains like
google.com.ua (for Ukraine),
google.ru (for Russia). But they use them only for search and maps and it doesn't actually change the language, it's something like country targeting, not language one. You still need to add
hl=xx in order to change the language.
Why they do this? They are contrary to their own recommendations.